1. Field of the Invention
The present invention relates to a laminated heat exchanger, and more particularly to a laminated heat exchanger used as an evaporator of a vehicle air conditioner, which is a refrigeration cycle on board a vehicle.
Herein and in the appended claims, the upper, lower, left-hand, and right-hand sides of FIG. 1 will be referred to as “upper,” “lower,” “left,” and “right,” respectively. The downstream side of flow (represented by arrow X in FIGS. 1, 2 and 9) of air is referred to as the “front,” and the opposite side as the “rear.”
2. Description of the Related Art
A known laminated heat exchanger includes a plurality of flat, hollow members arranged in a laminated condition (refer to Japanese Utility Model Publication (kokoku) No. 8-10764). Each of the flat, hollow members includes two vertically elongated metal plates having perimetric edge portions joined together. A bulging refrigerant flow tube portion having a hairpin shape is formed between the two metal plates. A bulging tank formation portion is formed continuously with each of opposite ends of the refrigerant flow tube portion. The tank formation portions of adjacent flat, hollow members are joined together. Clearances between the refrigerant flow tube portions of adjacent flat, hollow members serve as air-passing clearances. An oblong refrigerant outlet extending in a front-rear direction is formed in the outside wall of the tank formation portion of the flat, hollow member located at one end in the left-right direction. An outlet header is fixed to the outer surface of the outside wall of the tank formation portion of the endmost flat, hollow member. The outlet header includes a tubular body extending in the front-rear direction and having opposite end openings, and a closing member for closing one of the end openings of the body. A refrigerant passage hole communicating with the refrigerant outlet is formed in a side wall of the body of the outlet header. An outlet pipe having a circular cross section is connected to an open end portion of the body of the outlet header. The body of the outlet header includes a first portion which is a portion remaining after excluding from the body a portion located on a side toward the end opening and accounts for most of the body and in which the refrigerant passage hole is formed, a second portion which is the open end portion of the body and has a short, cylindrical shape, and a third portion which integrally connects the first portion and the second portion. The first portion has a rectangular cross section. A sleeve is disposed in such a manner as to extend into the second portion and into the outlet pipe, and is joined to the second portion and to the outlet pipe, whereby the outlet pipe is connected to the outlet header.
However, a vehicle air conditioner which employs the laminated heat exchanger disclosed in the above publication as an evaporator may suffer occurrence of abnormal noise caused by flow of refrigerant from the evaporator at the time of start-up of the vehicle air conditioner. This abnormal noise is known to be noise having a frequency of 5,000 Hz to 6,000 Hz.